The success of a sports turf grass sod (a mat of grass plants grown in surface soil and sliced horizontally into a thin layer for use in a place other than where grown) depends on the proper physical characteristics of the root zone medium (the medium in which the sod is initially grown) and the compatibility of that medium to the drainage bed and the root zone profiles (the area into which the root system of the sod will grow) underlying the sports field surface where the sod will be transplanted. Native topsoils used in sod production generally do not have the physical characteristics which make them compatible with the drainage beds and root zone profiles at the site of transplanting. Therefore, in most cases root zone medium must be provided to improve the compatibility of sod growing medium and the existing root zone profile. Typically, root zone medium is compounded from available sand, soil and fibrous organic amendments such as wood fiber. Because of extreme local variations in these materials, a high degree of expertise is necessary to determine which root zone medium blends contain the desired properties. Different lots of sand from the same pit may vary considerably in particle, size and shape. Native soils used in these blends also vary greatly in particle, size and shape, as well as in degree of aggregation, acidity, fertility, soluble salt, and organic matter content. Another variable in typical root zone medium blend is the fibrous organic amendment.
It has long been the desire of sports fields managers and golf course superintendents to have a source of sod in which the growth medium (root zone medium) matches or nearly matches and is thus compatible with the existing root zone profiles of the areas to be planted with sod.
Because of heavy compaction resulting from high traffic on sports fields and golf greens, sand is used extensively in root zone medium mixes. The proportion of sand to other materials in the mix will vary depending on what other amendments are to be used, the water percolation rate desired, and the ultimate use of the playing surface. Under most circumstances, if conventional sod is used on these playing surfaces, layering occurs. Layering refers to the formation of an interface between the fine soil particles of the root zone medium of the sod and the more coarse sand particles of the root zone profile of the transplant site. The layer formed by this process causes water flow to be interrupted when passing through the sod, into the root zone of the transplant site and the soil. As consistent percolation rates are very important in the maintenance of these surfaces and to the establishment of a suitable root system, great differences in particle size between the root zone medium of the sod and the root zone of the transplantation site which causes layering is obviously a great disadvantage.
The United States Golf Association (USGA) green section has established guidelines for sand particle sizes which, when used in golf greens, give the most consistent percolation rates, resists compaction by players and offers a good root zone environment for grass plants. These guidelines often work extremely well for other sports field applications but are occasionally modified to meet specific needs.
In U.S. Pat. No. 4,232,481, entitled "Carpet of Vegetable Matter" by Michel C. Chamoulaud, the production of sod or other vegetable matter is described. That patent teaches a compost layer made from wood bark which is crushed and gauged and spread onto a flat surface impermeable to plant roots. The compost mix is mixed with seeds before, during or after the application to the flat surface. The roots of the plants formed from the seed form a fabric embedded in a compost which facilitates the detachment of the sod from a flat surface.
In U.S. Pat. No. 4,941,282, by Gene Milstein entitled "Wildflower Sod Mat A Method of Propagation", the propagation of wildflower sod mats is described. The patent teaches a sod mat formed of sheets of porous synthetic material, a layer of planting medium and viable wildflower seeds which upon germination allows the root mass of the seeds to intermesh with the porous synthetic material thereby forming the sod mat. The patent teaches the planting medium composed of various materials such as a composition of 50% sphagnum moss 49% vermiculite or perlite, and 1% nutritive material, capable of sustaining plant growth.
The present invention is directed to a soil-less sand based root zone medium for the production of turf grass sod which has good percolation rates, good bulk density and resists compaction and whose composition may be altered so as to be compatible with the existing root zone profile of the transplant site. The present invention also relates to a method for production of turf grass sod using the soil-less sand based root zone medium. Finally the invention is also directed to a sod mat produced by the method of the present invention which is suitable for use on sports surfaces including stadium and golf courses.